This invention relates to a method for the production of a color developer and the product. Particularly, this invention relates to a new method for the production of a color developer useful in producing a copying sheet such as pressure-sensitive copying sheet and heat-sensitive copying sheet.
Several types of copying systems are known utilizing electron donor-acceptor color forming reaction between an electron donating colorless chromogenic material (hereinafter referred to as "color former") and an electron accepting acidic reactant material (hereinafter referred to as "color developer"). For example, the most typical pressure-sensitive copying systems are disclosed in U.S. Pat. Nos. 2,730,456, 2,730,457 and 3,672,935 and the heat-sensitive copying systems are disclosed in Japanese Pat. Publication Nos. 4160 of 1968 and 14039 of 1970 and British Pat. No. 1,056,365. Various forms of copying sheet are proposed and utilized.
As a color developer reacting with a color former such as triphenylmethane derivatives, fluoran derivatives and thiazine derivatives to form a colored image, there are known inorganic materials such as acid clay, bentonite, attapulgite, kaolin, fuller's earth and zeolite; physically or chemically treated inorganic materials such as activated clay, calcined kaolin and calcined activated clay; organic acid such as phenolic compounds, aromatic calboxylic acids for example benzoic acid, naphthoic acid and salicylic acid, and aromatic carboxylic acid derivatives; metallic compound of organic acids; mixture of organic acids and metal compounds such as zinc oxide and calcium carbonate; phenol-formaldehyde resin; salicylic acid-formaldehyde condensation product; styrene-maleic anhydride copolymer and metallic compound of the described above resinous materials. Generally, acids, acidic compounds toward color former on the theory of acid and base and materials oxidizing color former have been used as a color developer.
This invention relates to a method for the production of an improved color developer made from aromatic carboxylic acid as an essential component.
U.S. Pat. Nos. 2,900,388, 2,972,547 and 2,981,738 disclose the usage of salicylic acid, phenol, benzoic acid and the like as a color developer. Recording sheet applied with a particulate mixture comprising an organic carboxylic acid and/or polyvalent metal salt thereof and an organic high molecular compound compatible with them is disclosed in U.S. Pat. No. 3,924,027 by the inventors in this application.
An object of this invention is to provide a useful color developer essentially made from aromatic carboxylic acid, water-insoluble organic polymer and metal compound.
Another object of this invention is to provide a new method for the production of a color developer superior in color formability with activation of aromatic carboxylic acid.
Other objects and advantages of the invention will be apparent from the following description.